Method for producing antithrombotic coating material

ABSTRACT

Provided is a method for producing an antithrombotic coating material in which a high molecular weight polymer can be obtained by a solution polymerization using a radical polymerization initiator. The above-mentioned task is achieved by a method for producing an antithrombotic coating material, including steps of: preparing a methanol solution containing a monomer represented by formula (1): 
                         
wherein in formula (1), R 1 , R 2 , and R 3  are the same as those described in the specification, respectively; adding a radical polymerization initiator having a 10-hour half-life temperature of 60° C. or less to the methanol solution to prepare a polymerization reaction liquid; and polymerizing the monomer.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of priority of Japanese ApplicationNo. 2015-047610 filed on Mar. 10, 2015, Japanese Application No.2015-150087 filed on Jul. 29, 2015, and Japanese Application No.2016-000592 filed on Jan. 5, 2016, the entire content of which isincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method for producing anantithrombotic coating material.

BACKGROUND DISCUSSION

Recently, studies on medical materials utilizing various polymermaterials have been in progress, and their application to membranes forartificial kidney, membranes for blood plasma separation, catheters,stents, membranes for artificial lung, artificial blood vessels,anti-adhesion barriers, artificial skin, and the like, is possible. Forsuch applications, synthetic polymer materials, which are foreignmatters in the living body, are used in contact with biological tissue,or body fluid such as blood. Accordingly, it can be desirable for themedical materials to have biocompatibility. The desired biocompatibilityof the medical materials varies depending on their purpose or usage, butit can be desirable for medical materials used as materials in contactwith blood to have antithrombotic properties such as, for example,inhibition of the blood coagulation system, suppression of adhesion andactivation of platelets, and inhibition of activation of the complementsystem.

In general, impartment of the antithrombotic property to a medicalequipment is carried out by a method of coating a substrate constitutingthe medical equipment with an antithrombotic material (antithromboticcoating material), or a method of fixing an antithrombotic material tothe surface of the substrate.

For example, JP-A-4-152952 discloses a membrane for artificial organsand a medical equipment for use in contact with biological tissue orblood, which have, on their surfaces, a synthetic polymer that satisfieseffects of suppression of adhesion and activation of platelets, andinhibition of activation of the complement system, as well asbiocompatibility which is affinity with the biological tissue. InJP-A-4-152952, polymethoxyethyl acrylate (PMEA) or the like is disclosedas a synthetic polymer that is an antithrombotic material.

SUMMARY

Polymethoxyethyl acrylate (PMEA) is a hydrophilic polymer material thatis excellent in antithrombotic property and biocompatibility, andemployed as an antithrombotic component of a surface coating material ofa medical equipment in contact with blood. PMEA is hydrophilic, andthus, when used for the antithrombotic coating material, one having ahigher molecular weight can be desirable because the stability of thecoat layer increases.

As a polymerization method of PMEA, a solution polymerization using aradical polymerization initiator can be used. The solutionpolymerization is advantageous in that catalysts do not remain and thatit can be implemented at a low cost, but conventionally, a polymerhaving a high molecular weight was hardly obtained by the solutionpolymerization using a radical polymerization initiator.

The present disclosure has been made, for example, in view of the abovecircumstances. According to an exemplary aspect, provided is a methodfor producing an antithrombotic coating material in which a highmolecular weight polymer can be obtained by a solution polymerizationusing a radical polymerization initiator.

The present inventors have conducted extensive research, for example, toaddress the problems mentioned above. As a result, for example,disclosed is a method for producing an antithrombotic coating material,including steps of preparing a methanol solution containing a monomersuch as methoxyethyl acrylate, adding a radical polymerization initiatorhaving a 10-hour half-life temperature of 60° C. or less to the methanolsolution, and polymerizing the monomer.

According to the present disclosure, for example, there is provided amethod for producing an antithrombotic coating material in which a highmolecular weight polymer can be obtained by a solution polymerizationusing a radical polymerization initiator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of a cast film of an antithrombotic coatingmaterial containing the polymer obtained in Example 6, which is stainedwith phenol red, according to an exemplary aspect.

FIG. 2 is a photograph of a cast film of an antithrombotic coatingmaterial containing the polymer obtained in Comparative Example 2, whichis stained with phenol red.

FIG. 3A is a photograph depicting protein adsorption test results for anuntreated polypropylene film, according to an exemplary aspect.

FIG. 3B is a photograph depicting a film formed with a cast film of anantithrombotic coating material containing the polymer obtained inComparative Example 2.

FIG. 3C is a photograph depicting a film formed with a cast film of anantithrombotic coating material containing the polymer obtained inExample 7, according to an exemplary aspect.

DETAILED DESCRIPTION

According to an exemplary aspect, the present disclosure relates to amethod for producing an antithrombotic coating material, including stepsof preparing a methanol solution containing a monomer such asmethoxyethyl acrylate, adding a radical polymerization initiator havinga 10-hour half-life temperature of 60° C. or less to the methanolsolution to prepare a polymerization reaction liquid and polymerizingthe monomer. The production method according to the disclosure canincrease the molecular weight of the obtained polymer while employingthe solution polymerization using a radical polymerization initiator.When the molecular weight of the polymer contained in the antithromboticcoating material is high, the stability of the coat layer is enhanced.While not intended to limit the technical scope of the presentdisclosure, it is considered that the higher the molecular weight ofpolymers, the more easily polymers become entangled with each other, sothat the coat layer formed on a substrate is stabilized.

Hereinafter, exemplary embodiments of the disclosure will be described.The present disclosure is not limited to the following embodiments.

Further, in the present specification, the expression “X to Y”, whichrepresents a range, means “X or more and Y or less”. Unless otherwiseparticularly specified, operations and measurements of properties arecarried out under conditions of room temperature (20 to 25° C.) and arelative humidity of 40 to 50%.

An exemplary production method according to the disclosure includes astep of preparing a methanol solution containing a monomer representedby formula (1) below (methanol solution preparing step).

In formula (1), R¹ is a hydrogen atom or a methyl group, for example, ahydrogen atom.

In formula (1), R² is a cyclic, straight, or branched alkylene grouphaving 1 to 4 carbon atoms, for example, a straight or branched alkylenegroup having 1 to 4 carbon atoms. Specific examples thereof include amethylene group, an ethylene group, a trimethylene group, a propylenegroup, a cyclopropylene group, a tetramethylene group, and acyclobutylene group. Among them, in consideration of the effect ofenhancing the antithrombotic property, R² can be a straight or branchedalkylene group having 1 to 3 carbon atoms, for example, a methylenegroup or an ethylene group.

In formula (1), R³ is a cyclic, straight, or branched alkyl group having1 to 4 carbon atoms, for example, a straight or branched alkyl grouphaving 1 to 4 carbon atoms. Specific examples thereof include a methylgroup, an ethyl group, a propyl group, an isopropyl group, a n-butylgroup, a sec-butyl group, a tert-butyl group, and a cyclopropyl group.Among them, in consideration of the effect of enhancing theantithrombotic property, R³ can be a straight or branched alkyl grouphaving 1 to 3 carbon atoms, for example, a methyl group or an ethylgroup, for example, a methyl group. Specific examples of the monomerrepresented by formula (1) include methoxymethyl acrylate, methoxyethylacrylate (MEA), methoxypropyl acrylate, methoxybutyl acrylate,ethoxymethyl acrylate, ethoxyethyl acrylate, ethoxypropyl acrylate,ethoxybutyl acrylate, propoxymethyl acrylate, propoxyethyl acrylate,propoxypropyl acrylate, propoxybutyl acrylate, butoxymethyl acrylate,butoxyethyl acrylate, butoxypropyl acrylate, butoxybutyl acrylate,methoxymethyl methacrylate, methoxyethyl methacrylate, methoxypropylmethacrylate, methoxybutyl methacrylate, ethoxymethyl methacrylate,ethoxyethyl methacrylate, ethoxypropyl methacrylate, ethoxybutylmethacrylate, propoxymethyl methacrylate, propoxyethyl methacrylate,propoxypropyl methacrylate, propoxybutyl methacrylate, butoxymethylmethacrylate, butoxyethyl methacrylate, butoxypropyl methacrylate, andbutoxybutyl methacrylate. The monomer represented by formula (1) can bemethoxymethyl acrylate, methoxyethyl acrylate (MEA), ethoxymethylacrylate, ethoxyethyl acrylate, methoxymethyl methacrylate, methoxyethylmethacrylate, ethoxymethyl methacrylate, or ethoxyethyl methacrylate,and in terms of ease of availability, for example, methoxyethyl(meth)acrylate. These monomers may be used either alone or in mixture oftwo or more thereof.

In the present disclosure, “(meth)acrylate” means “acrylate” and/or“methacrylate.”

In the method according to the disclosure, in addition to the monomerrepresented by formula (1), other monomers that are copolymerizable withthe monomer represented by formula (1) (hereinafter, also referred to as“other monomers”) may be used. Examples of the other monomers that arecopolymerizable with the monomer represented by formula (1) includeacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide,aminomethylacrylate, aminoethylacrylate, aminoisopropylacrylate,diaminomethylacrylate, diaminoethylacrylate, diaminobutylacrylate,methacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide,aminomethylmethacrylate, aminoethylmethacrylate,diaminomethylmethacrylate, diaminoethylmethacrylate, methylacrylate,ethylacrylate, isopropylacrylate, butylacrylate, 2-ethylhexylacrylate,methylmethacrylate, ethylmethacrylate, butylmethacrylate, hexylacrylate,hexylmethacrylate, ethylene, and propylene.

When the other monomers are used in the methanol solution preparingstep, the ratio of the other monomers is, for example, 10 to 50 wt %,for example, 15 to 30 wt % based on the total monomers.

In an embodiment of the present disclosure, the monomer used in themethanol solution preparing step is the monomer represented by formula(1).

In the present disclosure, methanol is used as a main component of apolymerization solvent. If a solvent other than methanol is used as themain component of the polymerization solvent, for example, it isdifficult to increase the molecular weight of the polymer. While notintended to limit the technical scope of the present disclosure, it isconsidered that this is due to mobility of growing radicals during thepolymerization.

For example, the “methanol solution” in an exemplary embodiment cancontain methanol as the main component of the polymerization solvent,and a solvent other than methanol can be further included therein,within a range where a desired effect of the present disclosure is notimpaired. The expression “as the main component” means that methanolaccounts for 95 wt % or more, for example, 99 wt % or more (upper limit:100 wt %) in the whole solvent used in the methanol solution. Thepolymerization solvent other than methanol, which is contained in the“methanol solution”, may include one or more selected from, for example,water; alcohols such as ethanol, isopropanol, n-propanol, n-butanol,isobutanol, sec-butanol, tert-butanol, ethylene glycol, diethyleneglycol, propylene glycol, and dipropylene glycol; and organic solventssuch as chloroform, tetrahydrofuran, acetone, dioxane, and benzene, butnot limited thereto. When a solvent other than methanol is contained inthe “methanol solution”, the content of the solvent other than methanol(in a case where two or more kinds are contained, the total thereof) is,for example 5 parts by weight or less, for example, 1 part by weight orless based on 100 parts by weight of methanol.

In an exemplary embodiment, the polymerization solvent contained in the“methanol solution” is composed of methanol only. The content of themonomer represented by formula (1) that is contained in the methanolsolution can be 10 wt % or more, for example, 20 wt % or more, forexample, 25 wt % or more, for example, 30 wt % or more based on thewhole methanol solution, in terms of the magnitude of the resultingmolecular weight. Since the molecular weight of the resulting polymerincreases as the content of the monomer in the methanol solutionincreases, the upper limit of the content of the monomer represented byformula (1) in the methanol solution can be, for example, a saturatedconcentration or less, for example, 70 wt % or less, for example, 60 wt% or less. Further, when other monomers are contained in the methanolsolution, the whole monomer content (the total of the monomerrepresented by formula (1) and the other monomers) in the methanolsolution is, for example, a saturated concentration or less. At the timeof preparing the methanol solution, stirring may be carried out asdesired.

In the methanol solution preparing step, the methanol solution, to whichthe monomers have been added, may be subjected to a degassing treatmentprior to addition of a polymerization initiator. In the degassingtreatment, the methanol solution may be bubbled with an inert gas suchas, for example, nitrogen gas or argon gas for 0.5 to 5 hours. At thetime of the degassing treatment, the temperature of the methanolsolution may be adjusted to about 30° C. to 80° C., for example, apolymerization temperature in the subsequent polymerization step.

The method according to the disclosure includes a step of preparing apolymerization reaction liquid prepared by adding a radicalpolymerization initiator having a 10-hour half-life temperature of 60°C. or less to the methanol solution (the “polymerization reaction liquidprepared by adding a radical polymerization initiator having a 10-hourhalf-life temperature of 60° C. or less to the methanol solution” isalso referred to as a “polymerization reaction liquid”), andpolymerizing the monomer (polymerization step).

In the polymerization step, a radical polymerization initiator having a10-hour half-life temperature of 60° C. or less is used. When a radicalpolymerization initiator having a 10-hour half-life temperatureexceeding 60° C., such as 2,2′-azobisisobutyronitrile (AIBN, T10=65° C.)or dimethyl 2,2′-azobis(2-methylpropionate)(T10=66° C.), is used, it isnecessary to carry out the polymerization at a high temperatureexceeding 60° C. Therefore, when the monomer concentration is low, achain transfer reaction to the solvent, monomers, and polymers easilyoccurs in the radical polymerization, and thus, it is difficult toobtain a polymer having a high molecular weight. In addition, when themonomer concentration is high, since the polymerization is carried outat a high temperature, the polymerization rate is increased. Inaddition, since the growing radicals are hardly diffused, the polymeritself is gelled and insolubilized.

In the present disclosure, the “10-hour half-life temperature (T10)”means a temperature necessary for a concentration to decrease to half ofthe initial value (e.g., 0.01 mol/L) in 10 hours in a radically inertsolvent such as benzene.

Examples of the radical polymerization initiator having a 10-hourhalf-life temperature of 60° C. or less include, but are notparticularly limited to,2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (T10=30° C.),2,2′-azobis(2,4-dimethylvaleronitrile) (T10=51° C.),2,2′-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (T10=44° C.),2,2′-azobis[2-(2-imidazolin-2-yl)propane] disulfate dihydrate (T10=46°C.), 2,2′-azobis(2-methylpropionamidine) dihydrochloride (T10=56° C.),2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine)] hydrate (T10=57°C.), 3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate (T10=37° C.),α-cumyl peroxyneodecanoate (T10=38° C.), 1,1,3,3-tetrabutylperoxyneodecanoate (T10=44° C.), t-butyl peroxyneodecanoate (T10=48°C.), t-butyl peroxyneoheptanoate (T10=53° C.), t-butyl peroxypivalate(T10=58° C.), t-amyl peroxyneodecanoate (T10=46° C.), t-amylperoxypivalate (T10=55° C.), di(2-ethylhexyl) peroxydicarbonate (T10=49°C.), and di(secondary-butyl) peroxydicarbonate (T10=51° C.). Among them,exemplary is a radical polymerization initiator having a 10-hourhalf-life temperature of 50° C. or less, and exemplary is2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),3-hydroxy-1,1-dimethylbutylperoxyneodecanoate, or α-cumylperoxyneodecanoate, which has a very low 10-hour half-life temperatureof 40° C. or less. These radical polymerization initiators may becommercially available, and examples thereof include V-70 (T10=30° C.),V-65 (T10=51° C.), VA-044 (T10=44° C.), VA-046B (T10=46° C.), VA-50(T10=56° C.), and VA-057 (T10=57° C.) (all manufactured by Wako PureChemical Industries, Ltd.), AZO Series ADVN (T10=52° C.) (manufacturedby Otsuka Chemical Co., Ltd.), and Luperox™ 610 (T10=37° C.), Luperox™188 (T10=38° C.), Luperox™ 844 (T10=44° C.), Luperox™ 10 (T10=48° C.),Luperox™ 701 (T10=53° C.), Luperox™ 11 (T10=58° C.), Luperox™ 546(T10=46° C.), Luperox™ 554 (T10=55° C.), Luperox™ 223 (T10=49° C.), andLuperox™ 225 (T10=51° C.) (all manufactured by Arkema Yoshitomi, Ltd.).

The amount of the radical polymerization initiator having a 10-hourhalf-life temperature of 60° C. or less is, for example, 0.005 to 2parts by weight, for example, 0.1 to 0.5 parts by weight based on 100parts by weight of the monomer (in a case where two or more monomers areused, the total thereof). For example, when the amount of the radicalpolymerization initiator having a 10-hour half-life temperature of 60°C. or less is 0.005 parts by weight or more based on 100 parts by weightof the monomer, there is an advantage that a desired high molecularweight matter is obtained with a good reproducibility. For example, whenthe amount is 2 parts by weight or less, there is an advantage thatreduction in molecular weight is prevented.

The radical polymerization initiator may be added to methanol in anyconcentration, and followed by addition to the methanol solutioncontaining the monomer as an initiator methanol liquid. The content ofthe radical polymerization initiator in the initiator methanol liquidis, for example, 0.01 to 10 wt %.

In the initiator methanol liquid, a solvent other than methanol can beincluded therein, for example, within a range where a desired effect ofthe present disclosure is not impaired. For example, the initiatormethanol liquid may contain, for example, 5 parts by weight or less(e.g., 1 part by weight or less) of the solvent other than methanolbased on 100 parts by weight of methanol.

As for the content of the monomer represented by formula (1) containedin the polymerization reaction liquid in the polymerization step, thecontent of the monomer contained in the polymerization reaction liquidis, for example, 10 wt % or more based on the whole polymerizationreaction liquid, in terms of the magnitude of the resulting molecularweight. The content of the monomer contained in the polymerizationreaction liquid is, for example, 20 wt % or more, for example, 25 wt %or more, for example, 30 wt % or more based on the whole polymerizationreaction liquid. Since the molecular weight of the resulting polymerincreases as the content of the monomer in the polymerization reactionliquid increases, the upper limit of the content of the monomerrepresented by formula (1) in the polymerization reaction liquid is, butnot particularly limited to, for example, a saturated concentration orless, for example, 70 wt % or less, for example, 60 wt % or less. In anembodiment of the present disclosure, the content of the monomerrepresented by formula (1) contained in the polymerization reactionliquid is from 20 wt % to a saturated concentration. Further, when thepolymerization reaction liquid contains other monomers, the wholemonomer content (the total of the monomer represented by formula (1) andthe other monomers) in the polymerization reaction liquid is, forexample, a saturated concentration or less. At the time of preparing thepolymerization reaction liquid, stirring may be carried out asnecessary.

In terms of increase in molecular weight of the polymer and preventionof gelation in the polymerization step, the polymerization temperatureis, for example, a low temperature, but if excessively low, the progressof the reaction becomes slow, thereby lowering the productionefficiency. The polymerization temperature is, for example, 30 to 60°C., for example, 40 to 55° C.

The polymerization time is, for example, 1 to 24 hours, for example, 3to 12 hours at the above-mentioned polymerization temperature.

Furthermore, if desired, a polymerization rate regulator, a surfactant,and other additives may be used during the polymerization asappropriate.

The atmosphere in which the polymerization reaction is performed is notparticularly limited, but the polymerization reaction may be performedunder an air atmosphere, or an inert gas atmosphere such as nitrogen gasor argon gas. Further, the reaction liquid may be stirred during thepolymerization reaction.

The polymerized polymer may be purified by a general purification suchas re-precipitation, dialysis, ultrafiltration, or extraction.

The purified polymer may be dried by any method such as freeze drying,vacuum drying, spray drying, or heat drying, but in terms of reducingthe impact on the properties of the polymer, freeze drying or vacuumdrying is exemplary.

According to the solution polymerization using the radicalpolymerization initiator, it is possible to obtain a polymer having ahigh molecular weight. The weight average molecular weight of thepolymer obtained by the polymerization of the monomer is, for example,200,000 or more, for example, more than 300,000, for example, 400,000 ormore, in terms of the stability of the coat layer. The upper limit ofthe molecular weight of the polymer is, but not particularly limited to,for example, 1,000,000 or less, for example, less than 1,000,000, forexample, 800,000 or less in terms of the fact that the polymer itself,for example, is not gelled and insolubilized. In an exemplaryembodiment, the weight average molecular weight of the polymer obtainedby the polymerization of the monomer is more than 300,000 and 1,000,000or less.

The “weight average molecular weight” as used in the present disclosurecan be calculated by gel permeation chromatography (GPC) in terms ofpolystyrene as a standard material. Specifically, the polymer isdissolved in tetrahydrofuran (THF) to be 1 mg/ml. The GPCs of thestandard polystyrene and the polymer are measured by using a GPC systemLC-20 (manufactured by Shimadzu Corporation) equipped with a Shodex GPCcolumn LF-804 (manufactured by Showa Denko K.K.) and pouring THF as amoving phase. A calibration curve is plotted with the standardpolystyrene to thereby calculate the weight average molecular weight ofthe polymer.

The antithrombotic coating material obtained by the production methodaccording to the disclosure may include the polymer obtained by theabove-mentioned steps. The production method according to the disclosuremay further include a step of adding other additives such as a gellingagent, a thickener, a plasticizer, or a solvent to the polymer which isthen processed into a form such as a gel form or a solution form.Optionally, the production method may include a step of adding othercomponents such as a crosslinking agent, a thickener, a preservative, ora pH adjustor to the polymer to obtain a composition. When theantithrombotic coating material contains a crosslinking agent, thepolymer may be immobilized more firmly to a substrate surface.

When used in a form of a composition, a medium to be used is notparticularly limited; for example, the polymer can be dissolved,suspended, or dispersed therein, and examples thereof may include water,toluene, xylene, diethyl ether, chloroform, ethyl acetate, methylenechloride, tetrahydrofuran, acetone, acetonitrile, N,N-dimethylformamide,dimethyl sulfoxide, methanol, ethanol, propanol, n-butanol, ethyleneglycol, diethylene glycol, propylene glycol, and dipropylene glycol. Themedium may be used either alone or in mixture of two or more thereof.Among them, in terms of the solubility of the polymer, the solvent to beused is, for example, methanol.

The amount of the polymer contained in the composition may bearbitrarily set, or a solution obtained by dissolving the polymer to asaturation amount may be used. The amount of the polymer may be, forexample, 0.1 to 50 wt % based on the whole coating material.

An unreacted monomer contained in the antithrombotic coating materialis, for example, 0.01 wt % or less based on the whole polymer. The lowerlimit is not particularly limited because it is exemplary that theamount of the unreacted monomer is, for example, as small as possibleand may be, for example, 0 wt %. The content of the residual monomer maybe measured by a method known to those skilled in the art, such as, forexample, a high performance liquid chromatography.

In an exemplary embodiment of the present disclosure, there is providedan antithrombotic coating material including polyalkoxyalkyl(meth)acrylate that contains a structural unit (A) represented byformula (2) below, has a weight average molecular weight of 200,000 ormore (hereinafter, the “polyalkoxyalkyl (meth)acrylate that contains thestructural unit (A) represented by formula (2) below and has the weightaverage molecular weight of 200,000 or more” is also referred to as a“polymer according to the disclosure”), and is dissolved in methanol ora mixture of water and methanol. An exemplary embodiment relates to acomposition for imparting an antithrombotic property, containingpolyalkoxyalkyl (meth)acrylate that contains a structural unit (A)represented by formula (2) below and has a weight average molecularweight of 200,000 or more, and methanol or a mixture of water andmethanol. When the polyalkoxyalkyl (meth)acrylate contained in the coatlayer has a high molecular weight, for example, the stability of thecoat layer becomes excellent as described above.

In formula (2), R¹ represents a hydrogen atom or a methyl group, R²represents an alkylene group having 1 to 4 carbon atoms, and R³represents an alkyl group having 1 to 4 carbon atoms. For R¹, R², and R³in formula (2), the descriptions for R¹, R², and R³ described above forformula (1) are applied, respectively.

The antithrombotic coating material containing the hydrophilic materialhaving a high molecular weight as described above may be obtainedthrough the methanol solution preparing step and the polymerization stepdescribed above. For example, in the polymerization step, when thecontent of the monomer represented by formula (1), which is contained inthe polymerization reaction liquid, is set to 20 wt % or more,polyalkoxyalkyl (meth)acrylate having a weight average molecular weightof 200,000 or more may be obtained.

The weight average molecular weight of the polyalkoxyalkyl(meth)acrylate is, for example, more than 300,000, for example, 400,000or more in terms of the stability of the coat layer. The upper limit ofthe weight average molecular weight of the polymer is, but notparticularly limited to, for example, 1,000,000 or less, for example,less than 1,000,000, for example, 800,000 or less in terms of the factthat the polymer itself is not gelled and insolubilized. The “weightaverage molecular weight” of polyalkoxyalkyl (meth)acrylate can becalculated by gel permeation chromatography (GPC) in terms ofpolystyrene as a standard material.

Water absorbed into the polymer material is classified according to itsstate into free water (water frozen at 0° C. and having a weakinteraction with the polymer material or non-freezing water),intermediate water (water frozen at a temperature lower than 0° C. in atemperature rising process and having an intermediate interaction withthe polymer material or non-freezing water), or non-freezing water(water not frozen even at −100° C. due to a strong interaction with thepolymer material). For example, in a polymer material having a hydratedstructure in which a ratio of intermediate water is high, since thecontact of the hydrated structure of biological components such as bloodand the non-freezing water is suppressed, the hydrated structure of thebiological components is stably maintained. Therefore, the polymermaterial becomes more excellent in biocompatibility. The polyalkoxyalkyl(meth)acrylate is, for example, one in which a ratio of intermediatewater calculated by equation (1) below when equilibrium-hydrated exceeds32%. That is, in an exemplary embodiment of the present disclosure, anantithrombotic coating material is provided, in which a ratio ofintermediate water calculated by equation (1) below with respect to thepolyalkoxyalkyl (meth)acrylate that is equilibrium-hydrated(hereinafter, the “ratio of intermediate water calculated by equation(1) below when equilibrium-hydrated” is referred to as a “intermediatewater ratio”), exceeds 32%.Ratio (%) of Intermediate Water=(a/x)×100  [Equation (1)]:

In equation (1), a and x represents an intermediate water content (wt %)and an equilibrium water content (wt %), respectively, in thepolyalkoxyalkyl (meth)acrylate that is equilibrium-hydrated. Theexpression “equilibrium-hydrated” as used in the present disclosurerefers to a state where the water content of the polyalkoxyalkyl(meth)acrylate substantially reaches equilibrium in ultrapure water at25° C., for example, a state of being hydrated until a weight change perhour falls within ±1 wt %.

The intermediate water ratio described above may be determined by thefollowing method. That is, polyalkoxyalkyl (meth)acrylate is weighed toabout 0.1 g, and immersed in an excess amount (a weight at least 100times the weight of the polyalkoxyalkyl (meth)acrylate) of ultrapurewater at 25° C. for a week to thereby be equilibrium-hydrated. At thistime, it is confirmed that the weight change per hour falls within ±1 wt%. An appropriate amount of an equilibrium-hydrated sample is taken.After excess water on the surface of the sample is absorbed by alow-dust wiper, the sample is put on a glass petri dish that is weighedin advance, and is weighed within 3 minutes (W_(aq) (g)). Separately, anequilibrium-hydrated sample is dried under vacuum at 120° C. for 1 hour,left to cool in a desiccator for 30 minutes, and then, weighed (W_(dry)(g)). From the measured weight, an equilibrium water content (x, wt %)is calculated based on equation (2) below.

$\begin{matrix}{{{Equilibrium}\mspace{14mu}{water}\mspace{14mu}{content}\mspace{14mu}\left( {x,{{wt}\mspace{14mu}\%}} \right)} = {\frac{{W_{aq}(g)} - {W_{dry}(g)}}{W_{aq}(g)} \times 100}} & \left\lbrack {{Equation}\mspace{14mu}(2)} \right\rbrack\end{matrix}$

The equilibrium-hydrated sample is analyzed by a differential scanningcalorimetry (hereinafter, “DSC”) under the following conditions tothereby determine low-temperature crystallization and fusion behavior ofwater. Then, the water adsorbed onto the polymer material is classifiedinto free water, intermediate water, and non-freezing water, and a rateof each hydrated structure present in the sample is calculated from theequilibrium water content, a low-temperature crystallization heat(−ΔH_(cc)) at −40° C., and a fusion heat (−ΔH_(m)) at 0° C.Specifically, an intermediate water content (a, wt %), and optionally, afree water content (wt %) and a non-freezing water content (wt %) aredetermined.

(DSC Measurement Conditions)

Temperature range: −90° C. (maintained for 10 minutes)→50° C.

Temperature elevation rate: 2.5° C./min

Measurement atmosphere: Nitrogen 50 ml/min

Measurement Container: hermetic aluminum pan

Apparatus used: DSC Q100 manufactured by TA Instruments

(Calculation Method of Weight and Ratio of Each Hydrated Structure)

An equation “Equilibrium water content (wt %)=non-freezing water (wt%)+intermediate water (wt %)+free water (wt %)” is defined, and theweight and ratio of each hydrate structure are calculated by thefollowing method.

Intermediate water: −ΔH_(cc) (mJ) is divided by 334 J/g ofsolidification heat of water to obtain a weight (mg) of the intermediatewater. In addition, the weight of the intermediate water is divided byan amount of the measurement sample to obtain an intermediate watercontent (a, wt %).

Free water: −ΔH_(m) (mJ) is divided by 334 J/g of fusion heat of waterto obtain a total weight (mg) of the intermediate water and the freewater. The weight of the intermediate water is subtracted from the totalweight to obtain a weight (mg) of the free water. In addition, theweight of the free water is divided by a measurement sample amount toobtain a free water content (wt %).

Non-freezing water: The measurement sample amount (mg) is multiplied bythe equilibrium water content (x, wt %) to obtain an equilibrium wateramount (mg). The weight of the intermediate water and the weight of thefree water are subtracted from the equilibrium water amount to obtain aweight (mg) of the non-freezing water. In addition, the weight of thenon-freezing water is divided by the measurement sample amount to obtaina non-freezing water content (wt %).

When the polyalkoxyalkyl (meth)acrylate having a high intermediate waterratio as described above is used for the coating material, proteinadsorption or thrombus adhesion to the coat layer may be furthersuppressed. The intermediate water ratio in the polyalkoxyalkyl(meth)acrylate is, for example, 35% or more, for example, 37% or more.The upper limit of the intermediate water ratio is not particularlylimited (for example, upper limit: 100%).

The intermediate water ratio of the polyalkoxyalkyl (meth)acrylate maybe controlled, for example, by appropriately adjusting the weightaverage molecular weight. For example, the intermediate water ratio maybe increased by increasing the weight average molecular weight. Forexample, in a case of polymethoxyethyl acrylate (PMEA), the intermediatewater ratio may be controlled to a high intermediate water ratio higherthan 32% by setting the weight average molecular weight to be higherthan 90,000.

The structural unit (A) represented by formula (2) is derived from themonomer represented by formula (1). The polymer according to thedisclosure may contain structural units derived from the above-describedother monomers that are copolymerizable with the monomer represented byformula (1).

The polymer according to the disclosure may contain 50 to 100 mol % ofthe structural unit (A) in the whole constituent units (100 mol %), butthe polymer can contain 70 to 100 mol % of the structural unit (A), and,for example, is composed of the structural unit (A) (100 mol %). Whenthe ratio of the structural unit (A) is set within the range, theadhesion or the antithrombotic property of the coat layer may beenhanced.

The ratios of the structural unit (A) and structural units derived fromother monomers in the polymer according to the disclosure may bearbitrarily adjusted by changing the ratios of the monomers used in thepolymerization.

The terminal of the polymer according to the present disclosure is notparticularly limited and defined appropriately depending on the kind ofthe raw material used, and can be a hydrogen atom. When the polymeraccording to the disclosure is a copolymer, the structure of thecopolymer is also not particularly limited, but may be any of a randomcopolymer, an alternating copolymer, a periodic copolymer, or a blockcopolymer.

The ratios of the structural unit (A) and structural units derived fromother monomers in the obtained copolymer may be confirmed by an NMRmethod or infrared spectrum analysis. For example, in a case of acopolymer including the structural unit (A) and structural units derivedfrom other monomers, the ratios of the structural unit (A) andstructural units derived from other monomers in the copolymer may beanalyzed by an integral ratio in ¹H-NMR measurement. Further, when peaksare overlapped in ¹H-NMR measurement, the ratios may be determined using¹³C-NMR.

In the antithrombotic coating material according to the embodiment, thepolymer according to the disclosure is dissolved in methanol or amixture of water and methanol. As the medium that dissolves the polymeraccording to the disclosure, methanol or a mixture of water and methanolis used in terms of the solubility of the polymer. If other mediums areused, it can be difficult to dissolve the polymer according to thedisclosure at a desired concentration. When a mixture of water andmethanol is used as the medium, the volume ratio of water and methanolis not particularly limited as long as the polymer according to thedisclosure can be dissolved at a desired concentration, but the volumeratio (v/v) of water:methanol is, for example, 0.1:99.9 to 99:1 (v/v),for example, 80:20 to 99:1 (v/v), for example, 85:15 to 97:3 (v/v).

The amount of the polymer according to the disclosure contained in theantithrombotic coating material according to the embodiment may bearbitrarily set. For example, the polymer according to the disclosure iscontained in an amount of 0.01 to 50 wt %, for example, 0.1 to 50 wt %,for example, 0.2 to 10 wt % based on the whole coating material.

The polymer according to the disclosure may be dissolved in methanol ora mixture of water and methanol by using any suitable method withoutbeing particularly limited, for example, by a stirrer, a homogenizer, oran ultrasonication.

[Medical Equipment]

The antithrombotic coating material obtained by the production methodaccording to the disclosure, or the antithrombotic coating materialdissolved in methanol or a mixture of water and methanol according tothe disclosure is appropriately used in a medical equipment. That is, anembodiment of the disclosure relates to a medical equipment whichincludes a substrate and a coat layer on a substrate surface including acoating film of the antithrombotic coating material obtained by theproduction method according to the disclosure, or the antithromboticcoating material dissolved in methanol or a mixture of water andmethanol according to the disclosure.

Examples of the medical equipment include an intracorporeal implant typeartificial organs or therapeutic device, extracorporeal circulation typeof artificial organs, catheter, and a guide wire. Specific examplesthereof include implant type medical instruments such as an artificialblood vessel that is inserted into a blood vessel or lumen, anartificial trachea, a stent, artificial skin, and an artificialpericardium; artificial organ systems such as an artificial heartsystem, an artificial lung system, an artificial cardiopulmonary system,an artificial kidney system, an artificial liver system, and an immuneregulation system; catheters inserted or indwelled in a blood vesselsuch as an indwelling needle, an IVH catheter, a medicinal fluidadministrating catheter, a thermodilution catheter, an angiographiccatheter, a vasodilation catheter, and a dilator or an introducer; or, aguide wire for these catheters, or a stylet; and various suctioncatheters including a stomach tube catheter, a nutrition catheter, atube for intubation feeding (ED), a urinary catheter, a urethralcatheter, a balloon catheter, and an endotracheal suction catheter, orcatheters inserted or placed in a biological tissue other than a bloodvessel such as drainage catheter. For example, the antithromboticcoating material is appropriately used for an artificial lung system incontact with a large amount of blood, or an artificial cardiopulmonarysystem. For example, when a coat layer including a coating film of theantithrombotic coating material is formed on a hollow fiber membrane ofa hollow fiber membrane external blood perfusion type oxygenator, thethickness of the hollow fiber membrane (membrane thickness; a thicknessbetween the inner surface and the outer surface of the hollow fibermembrane) is, for example, 20 μm to 100 μm.

(Substrate)

The material of the substrate of the medical equipment is notparticularly limited, and examples thereof include various polymermaterials, for example, polyolefin or modified polyolefin such aspolyethylene, polypropylene, and ethylene-α-olefin copolymer; polyimide;polyimide; polyurethane; polyester such as polyethylene terephthalate(PET), polybutylene terephthalate (PBT), polycyclohexane terephthalate,and polyethylene-2,6-naphthalate; polyvinyl chloride; polyvinylidenechloride (PVDC); and fluororesin such as polytetrafluoroethylene (PTFE)and ethylene-tetrafluoroethylene copolymer (ETFE), metal, ceramics,carbon, and a composite material thereof. The polymer materialsdescribed above may be one that is subjected to a stretching processing(e.g., ePTFE).

The shape of the substrate is appropriately selected depending on theuse of the medical equipment, and may take a shape such as tubular,sheet-like, or rod-like. The form of the substrate is not limited to amolded body formed by using the above-described material alone, but ablended molding, an alloyed molding, or a multilayered molding is alsoavailable. The substrate may be mono-layered or laminated. When thesubstrate is laminated, substrates in respective layers may be the sameas or different from each other. When the substrate is swelled with asolvent such that the polymer is firmly immobilized, as the materialpresent at least on the substrate surface, the polymer material isexemplary because it can be satisfactorily swelled by the solvent.

The “substrate surface” as used in the disclosure refers to a substratesurface facing biological tissue or body fluid such as blood. When thecoat layer having the polymer is formed on the substrate surface, theantithrombotic property on the substrate surface is enhanced. In themedical equipment, the coat layer having the polymer is formed on thesubstrate surface facing biological tissue, or body fluid such as blood,but the coat layer may be formed on other surfaces.

In order to enhance the stability of the coat layer to the substratesurface, the substrate may be subjected to a surface treatment beforeforming the coat layer on the substrate surface. A method for thesurface treatment of the substrate includes, for example, a method ofirradiating active energy rays (electron beam, ultraviolet rays, X-rays,etc.), a method of utilizing a plasma discharge such as arc discharge,corona discharge, or glow discharge, and a method of applying a highelectric field, a method of applying ultrasonic vibrations through polarliquid (e.g., water), and a method of treating with ozone gas.

(Coat Layer)

In the medical equipment, a coat layer including a coating film of theantithrombotic coating material is formed on the substrate surface.

In the formation of the coat layer on the substrate surface, thesubstrate surface is coated by applying a coating liquid containing theantithrombotic coating material (e.g., the methanol dissolution liquidof the polymer according to the disclosure as described above). The term“coated” is intended to include a form in which the entire surface ofthe substrate is fully covered by the coat layer, as well as a form inwhich a part of the surface of the substrate is covered by the coatlayer, that is, a form in which the coat layer is attached to a part ofthe substrate surface.

As a method of applying the coating liquid containing the antithromboticcoating material on the substrate surface, any suitable method may beemployed, and examples thereof include, but are not particularly limitedto, dip coating, spraying, spin coating, dripping, doctor blade,brushing, roll coater, air knife coating, curtain coating, wire barcoating, and gravure coating.

The thickness of the coating liquid may be appropriately adjusteddepending on the use of the medical equipment, and is thinner than, forexample, 0.1 μm, but not particularly limited thereto.

By drying the substrate surface on which the coating liquid containingthe antithrombotic coating material is applied, the coat layer is formedon the substrate surface. The drying process may be appropriately set inconsideration of the glass transition temperature of the substrate, andis, for example, 0.5 to 10 hours at 20 to 80° C. Atmosphere in thedrying process is not particularly limited, but the drying process maybe performed under an air atmosphere, or an inert gas atmosphere such asnitrogen gas or argon gas.

EXAMPLES

The effects of the disclosure will be described using the followingexamples and comparative examples. However, the technical scope of thedisclosure is not limited to the following examples. Operations werecarried out at room temperature (25° C.) unless otherwise stated.

1. Preparation Example Example 1. Weight Average Molecular Weight ofPolymer: 140,000

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 80 g ofmethanol, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 50° C. for 1 hour to prepare amethanol solution (methanol solution preparing step). Then, to theMEA-dissolved methanol solution was added an initiator solution obtainedby dissolving 0.015 g of2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70, manufactured byWako Pure Chemical Industries, Ltd., 10-hour half-life temperature: 30°C.) in 5 g of methanol, to thereby prepare a polymerization reactionliquid (the monomer content in the polymerization reaction liquid: 15 wt%). Polymerization was carried out under a nitrogen gas atmosphere at50° C. for 5 hours while stirring the polymerization reaction liquid.The liquid after polymerization was added dropwise into ethanol toprecipitate a polymer, which was then recovered. The weight averagemolecular weight of the recovered polymer was 140,000.

Example 2. Weight Average Molecular Weight of Polymer: 200,000

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 55 g ofmethanol, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 50° C. for 1 hour to prepare amethanol solution (methanol solution preparing step). Then, to theMEA-dissolved methanol solution was added an initiator solution obtainedby dissolving 0.015 g of2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70, manufactured byWako Pure Chemical Industries, Ltd., 10-hour half-life temperature: 30°C.) in 5 g of methanol, to thereby prepare a polymerization reactionliquid (the monomer content in the polymerization reaction liquid: 20 wt%). Polymerization was carried out under a nitrogen gas atmosphere at50° C. for 5 hours while stirring the polymerization reaction liquid.The liquid after polymerization was added dropwise into ethanol toprecipitate a polymer, which was then recovered. The weight averagemolecular weight of the recovered polymer was 200,000.

Example 3. Weight Average Molecular Weight of Polymer: 250,000

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 40 g ofmethanol, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 50° C. for 1 hour to prepare amethanol solution (methanol solution preparing step). Then, to theMEA-dissolved methanol solution was added an initiator solution obtainedby dissolving 0.015 g of2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70, manufactured byWako Pure Chemical Industries, Ltd., 10-hour half-life temperature: 30°C.) in 5 g of methanol, to thereby prepare a polymerization reactionliquid (the monomer content in the polymerization reaction liquid: 25 wt%). Polymerization was carried out under a nitrogen gas atmosphere at50° C. for 5 hours while stirring the polymerization reaction liquid.The liquid after polymerization was added dropwise into ethanol toprecipitate a polymer, which was then recovered. The weight averagemolecular weight of the recovered polymer was 250,000.

Example 4. Weight Average Molecular Weight of Polymer: 320,000

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 30 g ofmethanol, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 50° C. for 1 hour to prepare amethanol solution (methanol solution preparing step). Then, to theMEA-dissolved methanol solution was added an initiator solution obtainedby dissolving 0.015 g of2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70, manufactured byWako Pure Chemical Industries, Ltd., 10-hour half-life temperature: 30°C.) in 5 g of methanol, to thereby prepare a polymerization reactionliquid (the monomer content in the polymerization reaction liquid: 30 wt%). Polymerization was carried out under a nitrogen gas atmosphere at50° C. for 5 hours while stirring the polymerization reaction liquid.The liquid after polymerization was added dropwise into ethanol toprecipitate a polymer, which was then recovered. The weight averagemolecular weight of the recovered polymer was 320,000.

Example 5. Weight Average Molecular Weight of Polymer: 410,000

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 25 g ofmethanol, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 50° C. for 1 hour to prepare amethanol solution (methanol solution preparing step). Then, to theMEA-dissolved methanol solution was added an initiator solution obtainedby dissolving 0.015 g of2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70, manufactured byWako Pure Chemical Industries, Ltd., 10-hour half-life temperature: 30°C.) in 3 g of methanol, to thereby prepare a polymerization reactionliquid (the monomer content in the polymerization reaction liquid: 35 wt%). Polymerization was carried out under a nitrogen gas atmosphere at50° C. for 5 hours while stirring the polymerization reaction liquid.The liquid after polymerization was added dropwise into ethanol toprecipitate a polymer, which was then recovered. The weight averagemolecular weight of the recovered polymer was 410,000.

Example 6. Weight Average Molecular Weight of Polymer: 420,000

80 g (0.61 mol) of methoxyethyl acrylate (MEA) was dissolved in 115 g ofmethanol, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 50° C. for 1 hour to prepare amethanol solution (methanol solution preparing step). Then, to theMEA-dissolved methanol solution was added an initiator solution obtainedby dissolving 0.08 g of 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile)(V-70, manufactured by Wako Pure Chemical Industries, Ltd., 10-hourhalf-life temperature: 30° C.) in 5 g of methanol, to thereby prepare apolymerization reaction liquid (the monomer content in thepolymerization reaction liquid: 40 wt %). Polymerization was carried outunder a nitrogen gas atmosphere at 50° C. for 5 hours while stirring thepolymerization reaction liquid. The liquid after polymerization wasadded dropwise into ethanol to precipitate a polymer, which was thenrecovered. The weight average molecular weight of the recovered polymerwas 420,000.

Example 7. Weight Average Molecular Weight of Polymer: 800,000

100 g (0.77 mol) of methoxyethyl acrylate (MEA) was dissolved in 95 g ofmethanol, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 50° C. for 1 hour to prepare amethanol solution (methanol solution preparing step). Then, to theMEA-dissolved methanol solution was added an initiator solution obtainedby dissolving 0.1 g of 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile)(V-70, manufactured by Wako Pure Chemical Industries, Ltd., 10-hourhalf-life temperature: 30° C.) in 5 g of methanol, to thereby prepare apolymerization reaction liquid (the monomer content in thepolymerization reaction liquid: 50 wt %). Polymerization was carried outunder a nitrogen gas atmosphere at 50° C. for 5 hours while stirring thepolymerization reaction liquid. The liquid after polymerization wasadded dropwise into ethanol to precipitate a polymer, which was thenrecovered. The weight average molecular weight of the recovered polymerwas 800,000.

Comparative Example 1. Weight Average Molecular Weight of Polymer:60,000

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 80 g oftoluene, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 80° C. for 1 hour to prepare a toluenesolution. Then, to the MEA-dissolved toluene solution was added aninitiator solution obtained by dissolving 0.015 g of dimethyl2,2′-azobis(2-methylpropionate) (V-601, manufactured by Wako PureChemical Industries, Ltd., 10-hour half-life temperature: 66° C.) in 5 gof toluene, to thereby prepare a reaction liquid (the monomer content inthe reaction liquid: 15 wt %). Polymerization was carried out under anitrogen gas atmosphere at 80° C. for 5 hours while stirring thereaction liquid. The liquid after polymerization was added dropwise inton-hexane to precipitate a polymer, which was then recovered. The weightaverage molecular weight of the recovered polymer was 60,000.

Comparative Example 2. Weight Average Molecular Weight of Polymer:90,000

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 55 g oftoluene, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 80° C. for 1 hour to prepare a toluenesolution. Then, to the MEA-dissolved toluene solution was added aninitiator solution obtained by dissolving 0.015 g of dimethyl2,2′-azobis(2-methylpropionate) (V-601, manufactured by Wako PureChemical Industries, Ltd., 10-hour half-life temperature: 66° C.) in 5 gof toluene, to thereby prepare a reaction liquid (the monomer content inthe reaction liquid: 20 wt %). Polymerization was carried out under anitrogen gas atmosphere at 80° C. for 5 hours while stirring thereaction liquid. The liquid after polymerization was added dropwise inton-hexane to precipitate a polymer, which was then recovered. The weightaverage molecular weight of the recovered polymer was 90,000.

Comparative Example 3. Weight Average Molecular Weight of Polymer:120,000

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 40 g oftoluene, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 80° C. for 1 hour to prepare a toluenesolution. Then, to the MEA-dissolved toluene solution was added aninitiator solution obtained by dissolving 0.015 g of dimethyl2,2′-azobis(2-methylpropionate) (V-601, manufactured by Wako PureChemical Industries, Ltd 10-hour half-life temperature: 66° C.) in 5 gof toluene, to thereby prepare a reaction liquid (the monomer content inthe reaction liquid: 25 wt %). Polymerization was carried out under anitrogen gas atmosphere at 80° C. for 5 hours while stirring thereaction liquid. The liquid after polymerization was added dropwise inton-hexane to precipitate a polymer, which was then recovered. The weightaverage molecular weight of the recovered polymer was 120,000.

Comparative Example 4

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 30 g oftoluene, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 80° C. for 1 hour to prepare a toluenesolution. Then, to the MEA-dissolved toluene solution was added aninitiator solution obtained by dissolving 0.015 g of dimethyl2,2′-azobis(2-methylpropionate) (V-601, manufactured by Wako PureChemical Industries, Ltd., 10-hour half-life temperature: 66° C.) in 5 gof toluene, to thereby prepare a reaction liquid (the monomer content inthe reaction liquid: 30 wt %). Immediately after the addition of theradical polymerization initiator, rapid elevation of the temperature andviscosity was confirmed, and gelation of the reaction liquid occurred.Thus, heating and stirring were stopped.

Comparative Example 5

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 25 g oftoluene, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 80° C. for 1 hour to prepare a toluenesolution. Then, to the MEA-dissolved toluene solution was added aninitiator solution obtained by dissolving 0.015 g of dimethyl2,2′-azobis(2-methylpropionate) (V-601, manufactured by Wako PureChemical Industries, Ltd., 10-hour half-life temperature: 66° C.) in 3 gof toluene, to thereby prepare a reaction liquid (the monomer content inthe reaction liquid: 35 wt %). Immediately after the addition of theradical polymerization initiator, rapid elevation of the temperature andviscosity was confirmed, and gelation of the reaction liquid occurred.Thus, heating and stirring were stopped.

Comparative Example 6. Weight Average Molecular Weight of Polymer:90,000

15 g (0.115 mol) of methoxyethyl acrylate (MEA) was dissolved in 40 g oftoluene, and the obtained solution was introduced into a four-neckedflask, followed by N₂ bubbling at 50° C. for 1 hour to prepare a toluenesolution. Then, to the MEA-dissolved toluene solution was added aninitiator solution obtained by dissolving 0.015 g of2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70, manufactured byWako Pure Chemical Industries, Ltd., 10-hour half-life temperature: 30°C.) in 5 g of toluene, to thereby prepare a reaction liquid (the monomercontent in the reaction liquid: 25 wt %). Polymerization was carried outunder a nitrogen gas atmosphere at 50° C. for 5 hours while stirring thereaction liquid. The liquid after polymerization was added dropwise intohexane to precipitate a polymer, which was then recovered. The weightaverage molecular weight of the recovered polymer was 90,000.

TABLE 1 Polymerization Solvent Methanol Toluene Toluene Polymerization50° C. 50° C. 80° C. Temperature 10-hour half-life 30° C. 30° C. 66° C.Temperature of Polymerization Initiator Content of 15 wt % Ex. 1 Mw.Comp. Mw. 60,000 Polymer 140,000 Ex. 1 20 wt % Ex. 2 Mw. Comp. Mw.90,000 200,000 Ex. 2 25 wt % Ex. 3 Mw. Comp. Mw. Comp. Mw. 120,000250,000 Ex. 6 90,000 Ex. 3 30 wt % Ex. 4 Mw. Comp. Gelled 320,000 Ex. 435 wt % Ex. 5 Mw. Comp. Gelled 410,000 Ex. 5 40 wt % Ex. 6 Mw. 420,00050 wt % Ex. 7 Mw. 800,000

2. Antithrombotic Test

(Formation of Coat Layer)

The polymers obtained in Examples 2, 3, and 5, and Comparative Example 2were each dissolved in methanol to a concentration of 1 wt %. Each ofePTFE-made artificial blood vessels (inner diameter: 5 mm, outerdiameter: 7 mm, overall length: 5 cm) was immersed in the methanolsolution described above, and allowed to stand for 5 minutes. Theartificial blood vessel was taken out from the methanol solution, anddried by heating in an oven set at 60° C. for 3 to 4 hours to therebyform a coat layer.

(Antithrombotic Test)

A soft vinyl chloride tube (inner diameter: 6 mm, overall length: 27 cm)was connected with polycarbonate connectors at its both ends.Furthermore, one of the connectors was connected with one end of each ofthe artificial blood vessels on which the coat layer was formed asdescribed above. The lumen of the soft vinyl chloride tube was filledwith 4.5 ml of human blood having anticoagulability enhanced withheparin (heparin concentration: 0.2 units/ml). Thereafter, the connectorside which was not connected with the artificial blood vessel and theend of the artificial blood vessel side which was not connected with theconnector, were connected with each other to form a loop. The loop wasfixed to a cylindrical rotator, and allowed to circulate blood in thelumen of the loop at room temperature (25° C.) in 14 revolutions/min for120 minutes. The artificial blood vessel was removed from the loop, thelumen of the artificial blood vessel was washed with a physiologicalsaline solution, and thrombus formed on the lumen surface (blood contactsurface) was immobilized (25° C.) with 1 wt % aqueous glutaraldehydesolution. After the immobilization, the artificial blood vessel waswashed with water and dried, and the blood contact surface of theartificial blood vessel was observed by an electron microscope toconfirm the extent of the thrombus formation. A ratio of the area coatedby the thrombus formed was calculated based on the area of the entireobservation screen by the electron microscope. The results are shown inTable 2.

TABLE 2 Surface Observation Result After Blood Polymer used forFormation Circulation (Level of of Coat Thrombus Formation*) TestExample 1 Example 2 (Mw. 200,000) 1 Test Example 2 Example 3 (Mw.250,000) 1 Test Example 3 Example 5 (Mw. 410,000) 1 Test Example 4 Comp.Example 2 (Mw. 3 90,000) Test Example 5 No Coat 4 *4: Coated Area 100%3: 50% ≤ Coated Area < 100% 2: 20% ≤ Coated Area < 50% 1: Coated Area <20%

As shown in Table 2, the thrombus formation was suppressed by using theantithrombotic coating material containing a high molecular weightpolymer. This indicates that the coat layer formed by the coating filmof the antithrombotic coating material is stable.

3. Blood Circulation Test

According to the following method, the antithrombotic property wasevaluated on a substrate (a porous hollow fiber membrane for gasexchange, made of porous polypropylene; thickness of hollow fiber: 25μm) coated with the polymer having a weight average molecular weight of410,000, obtained in Example 5. That is, the polymer was dissolved in amixture of water and methanol (water:methanol=95:5 (v/v)) to aconcentration of 0.05 wt %, to thereby obtain a coating material (coatliquid). The coating material was filled in a simulated product form(blood circulation module) from a blood import side, and left to standfor 120 seconds. Thereafter, the coating material was removed from theblood circulation module, and dried by blowing air at room temperature(25° C.) for 240 minutes to thereby form a coat layer. This bloodcirculation module was incorporated into an extracorporeal circulationcircuit, and filled with a dilute human fresh blood (heparin: 0.2units/ml) obtained by mixing 90 ml of heparin (0.45 units/ml)-addedhuman fresh blood and 110 ml of saline solution. The dilute human freshblood was circulated in the blood circulation module at room temperature(25° C.) in 500 ml/min. After 60 minutes from the circulation start,blood was sampled from the blood circulation circuit, the platelet countwas measured, and a ratio of the platelet count after the circulation tothe platelet count before the circulation start (100%) (platelet countmaintenance rate) was determined. As a result, the platelet countmaintenance rate was 91%.

In the blood circulation module coated with the coating materialcontaining the polymer of Example 5, the platelets were maintained at ahigh maintenance rate. That is, it was confirmed that reduction inplatelet count due to coagulation of platelets originated fromactivation of the coagulation system and the platelet system, oradhesion to a substrate, was decreased, and the antithrombotic propertywas excellent.

4. Cast Film Formability Test

The polymer (weight average molecular weight=420,000) synthesized inExample 6 was dissolved in methanol such that the concentration of thepolymer became 1 wt % (coating material (1)). Separately, the polymer(weight average molecular weight=90,000) synthesized in ComparativeExample 2 was dissolved in methanol such that the concentration of thepolymer became 1 wt % (coating material (2)). For the coating material(1) and the coating material (2), a cast film was fabricated by thefollowing method, and the formability of the film was evaluated.

A biaxially stretched polypropylene film having a thickness of 50 μm anda size of 10 cm×cm was prepared. Onto the polypropylene film, 0.1 g of acoating material was added dropwise, and dried at room temperature (25°C.) for 5 hours to form a coat layer (cast film) on the polypropylenefilm. Subsequently, the coat layer (cast film) was stained with anaqueous solution of phenol red, and the shape of the cast film wasobserved.

The cast film fabricated with the coating material (1) was maintained ina circular shape, and the cast film was stable. In contrast, the castfilm fabricated with the coating material (2) was not maintained in aneat film shape. In coating material (1), it was considered that thepolymer had a high molecular weight so that mutual entanglement ofmolecular chains was increased, thereby forming a strong cast film.

5. Analysis of Hydrated Structure

The polymers obtained in Example 3, Example 5, Example 7, andComparative Example 2 were each weighed to about 0.1 g, and immersed inan excess amount (a weight 100 times the weight of the polymer) ofultrapure water at 25° C. for a week to thereby be equilibrium-hydrated.It was confirmed that the weight change per hour fell within ±1 wt %. Anappropriate amount of each equilibrium-hydrated sample was taken. Afterexcess water on the surface of the sample was absorbed by a low-dustwiper, the sample was put on a glass petri dish that was weighed inadvance, and was weighed within 3 minutes (W_(aq) (g)). Separately, anequilibrium-hydrated sample was dried under vacuum at 120° C. for 1hour, left to cool in a desiccator for 30 minutes, and then, weighed(W_(dry) (g)). From the measured weight, an equilibrium water content(x, wt %), an intermediate water content (a, wt %), a free water content(wt %), and a non-freezing water content (wt %) were calculated by themethod described above.

TABLE 3 Inter- Non- Ratio of Weight mediate Free freezing Inter- Averagewater water Water mediate molecular content content Content water weight(wt %) (wt %) (wt %) (%) Example 3 250,000 3.1 2.8 3.2 34 Example 5410,000 3.3 1.8 3.8 37 Example 7 800,000 3.4 0.6 3.3 47 Comparative90,000 3.0 4.5 1.8 32 Example 2

6. Protein Adsorption Test

The polymers of Example 7 and Comparative Example 2 were each dissolvedin methanol such that the final concentration reached 1 wt %, to therebyprepare a coating material (3) (Mw=800,000) and a coating material (4)(Mw=90,000). The coating material (3) or the coating material (4) wascast on a biaxially stretched polypropylene film (FOP50, manufactured byFutamura Chemical CO., LTD.; thickness: 50 μm), and then, left to standfor drying at room temperature (25° C.) for 48 hours or more.Thereafter, the protein adsorption test was carried out according to thefollowing procedure. In addition, for comparison, the same test wascarried out using a biaxially stretched polypropylene film on which nocast film was formed.

Each film was immersed in a TBS solution containing BSA (bovine serumalbumin, manufactured by Sigma Co., Ltd.) at a concentration of 1 wt %,and shaken at room temperature (25° C.) for 1 hour. Thereafter, the filmwas immersed in a TBS-T diluent, and washed for 5 minutes. Washing wasrepeated three times. Subsequently, the film was immersed in a solutionof 5 wt % of skimmed milk (manufactured by Wako Pure ChemicalIndustries, Ltd.) in TBS, and shaken at room temperature (25° C.) for 1hour, followed by blocking. The film was immersed in a TBS-T diluent,and washed for 5 minutes. Washing was repeated three times.Subsequently, the film was immersed in a diluent (antibodyconcentration: 5 μg/ml) of a primary antibody (rabbit anti-bovinealbumin antibody, manufactured by BETHYL laboratories, Inc.), and shakenat room temperature (25° C.) for 2 hours. The film was immersed in aTBS-T diluent, and washed for 5 minutes. Washing was repeated threetimes. The film was immersed in a diluent (a 100-fold antibody dilutionof stock solution) of a gold-labeled secondary antibody (goatanti-rabbit IgG antibody, manufactured by KPL laboratories, Inc.), andshaken at room temperature (25° C.) for 2 hours. The film was immersedin a TBS-T diluent, and washed for 5 minutes. Washing was repeated threetimes. Thereafter, sensitization of adsorbed gold was carried out by asilver enhancer kit (manufactured by Sigma Co., Ltd.). After platinumdeposition on the sensitized surface, observation was made with ascanning electron microscopy (apparatus name: S-3400N, manufactured byHitachi High-Technologies Corporation, magnification: 5,000 times). Thecompositions of the TBS and the TBS-T diluent are as follows.

TBS: 24.2 g of Tris (trishydroxymethylaminomethane) and 80 g of NaClwere dissolved in pure water, and the pH was adjusted to 7.6 with HCl.Pure water was added up to a total volume of 1 L (0.2 M Tris).

TBS-T diluent: Tween™ was dissolved in the TBS such that the finalconcentration reached 0.05 wt %.

The results are illustrated in FIG. 3. As illustrated in FIG. 3, ascompared with the cast film having a coat layer formed of a coatingmaterial 4 (FIG. 3b ), in the cast film having a coat layer formed of acoating material 3 (FIG. 3c ), silver particles are substantially notobserved, and a protein adsorption amount was very small. It has beenfound that, in a case of being equilibrium-hydrated, the coatingmaterial containing polyalkoxyalkyl (meth)acrylate with a highproportion of intermediate water, has an excellent coatability and avery small protein adsorption amount.

The detailed description above describes exemplary aspects of methodsfor producing an antithrombotic coating material and antithromboticcoating materials. The invention is not limited, however, to the preciseembodiments and variations described. Various changes, modifications andequivalents can be effected by one skilled in the art without departingfrom the spirit and scope of the invention as defined in theaccompanying claims. It is expressly intended that all such changes,modifications and equivalents which fall within the scope of the claimsare embraced by the claims.

What is claimed is:
 1. A method for producing an antithrombotic coating material, the method comprising: preparing a methanol solution containing a monomer consisting of methoxymethyl acrylate, methoxyethyl acrylate (MEA), ethoxymethyl acrylate, ethoxyethyl acrylate, methoxymethyl methacrylate, methoxyethyl methacrylate, ethoxymethyl methacrylate, ethoxyethyl methacrylate, or a combination thereof; adding a radical polymerization initiator having a 10-hour half-life temperature of 60° C. or less to the methanol solution to prepare a polymerization reaction liquid, wherein the radical polymerization initiator having a 10-hour half-life temperature of 60° C. or less is 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile); and polymerizing the monomer to form a polymer, wherein the monomer used to form the polymer consists of methoxymethyl acrylate, methoxyethyl acrylate (MEA), ethoxymethyl acrylate, ethoxyethyl acrylate, methoxymethyl methacrylate, methoxyethyl methacrylate, ethoxymethyl methacrylate, ethoxyethyl methacrylate, or a combination thereof.
 2. The method according to claim 1, wherein a content of the monomer contained in the polymerization reaction liquid is 10 wt % or more.
 3. The method according to claim 2, wherein the content of the monomer contained in the polymerization reaction liquid is from 20 wt % to a saturated concentration.
 4. The method according to claim 1, wherein a weight average molecular weight of the polymer obtained by the polymerization of the monomer is 200,000 or more.
 5. The method according to claim 4, wherein the weight average molecular weight of the polymer obtained by the polymerization of the monomer is more than 300,000 but not more than 1,000,000.
 6. The method according to claim 1, wherein the methanol solution contains methanol in an amount of 95 wt % or more, based on the total solvent content of the methanol solution.
 7. The method according to claim 1, wherein the radical polymerization initiator having a 10-hour half-life temperature of 60° C. or less is added in an amount of 0.005 to 2 parts by weight of the monomer.
 8. The method according to claim 1, wherein the content of the monomer contained in the polymerization reaction liquid is 10 wt % or more and 70 wt % or less.
 9. The method according to claim 1, wherein a weight average molecular weight of the polymer obtained by the polymerization of the monomer is 200,000 or more, and wherein the radical polymerization initiator having a 10-hour half-life temperature of 60° C. or less is added in an amount of 0.005 to 2 parts by weight of the monomer.
 10. The method according to claim 1, wherein the monomer consists of methoxyethyl acrylate. 